DE 10 2007 006 477 A1 discloses a method for determining the internal resistance of a vehicle battery. The method serves for monitoring the state of health of an electrical energy store of a vehicle, in particular of a vehicle battery or of a supercapacitor, by means of ascertaining the internal resistance Ri of the energy store. In the method, the internal resistance is determined by way of a voltage alteration of the voltage of the energy store as a result of the turning on or off of a load RLi connected to the on-board electrical system of the vehicle, wherein the voltage of the energy store Uo is measured with the load RLi switched off and the voltage UBat of the energy store is measured with the load switched on and a voltage difference ΔUBat is determined therefrom, wherein the internal resistance Ri is determined by the formula Ri=ΔUBat/Uo×RLi.